Pollution Factors of the Upper Willamette Watershed

A comparison of point and non-point source pollution between the McKenzie River Watershed and the Upper Willamette Watershed. This data demonstrates the increased need for pollution mitigation efforts upstream of the new EWEB facility on the Willamette River, as this river is significantly more polluted than the McKenzie.

The city of Eugene has excellent water quality due to the cleanliness of the McKenzie River and the efforts of EWEB to keep it so. While the McKenzie provides excellent water, it is Eugene’s only source of water. Should a toxic event occur in or near the river, the people of Eugene would not have a reliable source of clean water. Besides supporting pollution mitigation projects within the McKenzie, EWEB is also constructing a secondary water filtration plant on the Willamette River. This station, located just downstream of the confluence of the Coast and Middle Fork, will have to filter out more pollutants than its counterpart on the McKenzie. This is due to the different land use and point source pollution within the Coast and Middle Fork watersheds. There is a variety of pollution found in the water by the time it flows by the station:

As rivers flow through urban areas they are polluted with runoff contaminated with motor oil and rubber fragments (Foldvik et al 2022). As it flows further it can be polluted by the town's wastewater, which can contain elevated levels of phosphorus, estrogen, or even E. Coli (Elliot et al 2011). As the river enters the countryside it is polluted by runoff from adjacent agricultural land. This can be in the form of bacteria and phosphorus from manure, oversprayed or leached pesticides, and excess nitrogen and phosphorus from fertilizers (Metson et al 2020).

To mitigate the impacts to water quality, EWEB should support similar water quality protection efforts in the Coast and Middle Forks to those they support in the McKenzie.

  The Coast Fork has the highest and most spread out population and highest population density (US Census 2020). 

While there are significant populations in the McKenzie and Middle Fork watersheds, they are clustered in and around Springfield, with smaller populations upriver (ie Oakridge). I5 runs through the Coast Fork watershed, with Annual Average Daily Traffic (AADT) at 41,753 in 2023. The AADT of Highway 58 (Middle Fork) in 2023 was 28,140. Highway 126 in the McKenzie watershed experienced an AADT of 39,153 in 2023 (OR DOT 2024). 

The Middle Fork and McKenzie River watersheds have a similar proportion of protected land (mostly Willamette National Forest), roughly 80%, while the Coast Fork watershed has less than half that (USGS 2022).

The Coast Fork watershed has a higher count for all surveyed pollution point sources (OR DEQ 2024). These sources include Solid Waste Facilities, Underground Fuel Tanks, Active EPA Contaminated Sites, Industrial Wastewater Outflows, and Confined Animal Feeding Operations.

The landcover within the 100 year floodplain has a significant impact on the quality of a river's water. The top land use of the Coast Fork’s floodplain is 45% pasture/hay, to the Middle Fork’s 17% and the McKenzie’s 32% (USGS 2024). 

5.15% of the McKenzie’s 100 year floodplain has been developed, compared to 4.09% of the Middle Fork floodplain and 9.32% of the Coast Fork floodplain.

  The Middle Fork of the Willamette River has very similar characteristics to the McKenzie River. One could expect a similar pollution rate between both rivers. The Coast Fork has a smaller drainage, but larger and more dispersed populations, more pollution point sources, and less protected lands. The Coast Fork also has a lower annual flow than the Middle Fork, so the water is likely to have a higher pollution rate. If EWEB plans to support water quality protection efforts, it should focus on efforts in the Coast Fork of the Willamette River watershed. 

Citations

US Geological Survey (2024) National Hydrology Database Plus https://www.arcgis.com/home/item.html?id=f1f45a3ba37a4f03a5f48d7454e4b654

US Geological Survey (2024) National Land Cover Database

https://www.arcgis.com/home/item.html?id=3ccf118ed80748909eb85c6d262b426f

US Geological Survey (2022) National Gap Analysis Program

https://www.sciencebase.gov/catalog/item/61794fc2d34ea58c3c6f9f69

OR Department of Environmental Quality (2024) GIS Resources https://www.oregon.gov/deq/Get-Involved/Pages/GIS.aspx

OR Department of Transportation (2024) “Detailed State Highway Segment Traffic Data 2023” 

https://www.oregon.gov/ODOT/Data/Pages/Traffic-Counting.aspx

US Census Bureau (2020) “Population” US Census Blocks

https://www.arcgis.com/home/item.html?id=d795eaa6ee7a40bdb2efeb2d001bf823